1. Field of the Invention
The present invention relates to a switching mode power supply and its method of driving.
2. Description of the Related Art
A switching mode power supply (hereinafter referred to as an “SMPS”) is a device that rectifies an input AC voltage to an output DC voltage (DC-link voltage) and that converts the input DC voltage to an output DC voltage having another level. The output DC voltage can be higher or lower than the input DC voltage. SMPSs are often used in battery powered devices such as power electric devices, mobile phones and laptop computers.
In general, an SMPS can include a transformer and has a switching transistor at a primary side of a transformer that receives a DC voltage and controls the duty of the switching transistor. SMPSs can use a feedback loop to transfer a voltage or a current of an output unit to the primary side of the transformer e.g. through an opto-coupler or through a shunt regulator that is connected to the output side of the transformer. Application of such transfer loops allows delivering a regulated output DC voltage through the output unit.
However, since opto-couplers and shunt regulators are expensive and large, it is difficult to highly integrate SMPSs into circuits and contain cost.